1. Field of the Invention
The present invention relates to an edge switch and, more particularly, to a voice-quality guaranteeing edge switch wherein provisions are made to consistently maintain stable and good voice quality by avoiding congestion in a connectionless packet communication network such as an IP network. In the description given hereinafter, an IP network will be taken as a representative example of the connectionless packet communication network.
2. Description of the Related Art
In recent years, with the explosive proliferation of IP networks, these has been a transition from traditional networks primarily intended for voice communication, which use expensive switching equipment, toward IP network-based services which use inexpensive routers and which are primarily intended for data communication with the additional capability of voice communication.
FIG. 1 is a diagram showing the configuration of an IP network which forms the background of the present invention. In the figure, reference numeral 11 is the IP network, 121 to 124 are edge switches, 131 to 134 are VoIP terminals, and 141 to 143 are video telephone terminals. The VoIP terminals and the video telephone terminals may be replaced by personal computers equipped with IP telephone functions.
The IP network has the advantage that a variety of media, such as voice, moving video images, and data, can be transferred at low cost, but when it comes to voice communication, it is difficult to consistently maintain voice quality comparable to that of fixed telephones, because the IP network is based on connectionless transfer technology.
There are services that are primarily intended to provide data transfer service, with voice transfer service provided as a value added service; in the case of such services, there is no need to ensure particularly high voice quality, but if services are to be provided that are primarily intended for voice communication that can replace the existing public telephone network, it becomes necessary to ensure high quality voice communication comparable to that of fixed telephones as represented by the Class A standard provided by the Ministry of Internal Affairs and Communications of Japan.
In that case, previously, it has been practiced to guarantee voice quality by theoretically computing congestion information such as packet delay, packet loss, packet jitter, etc. according to the installation places of routers and the number of installed router stages in a network during the design stage of the network, and by objectively measuring the voice quality between users at their respective premises by using, for example, the PSQM (Perceptual Speech Quality Measure) recommended by the ITU-T P.861.
[Patent Document] Japanese Unexamined Patent Publication No. 2002-204278
[Patent Document] Japanese Unexamined Patent Publication No. 2002-281078
[Patent Document] Japanese Unexamined Patent Publication No. 2004-722442
However, unlike the traditional public network that guarantees circuit bandwidth, in IP networks, which employ connectionless transfer schemes, packet loss, jitter, and delay occur in the event of unexpected congestion or local or global congestion, or in the case of chronic congestion, and these can cause serious voice quality degradation.
Furthermore, in IP networks which employ connectionless transfer schemes, emergency communication calls and important communication calls which, in the public network, must be given precedence over all other calls may not be properly served in the event of serious degradation of voice quality, and this can pose a threat to stable social life.
One possible method to address these problems would be to avoid the occurrence of congestion by increasing the capacity of the network itself and providing higher speed and broader bandwidth, but it would not be realistic to construct an IP network that could prevent the occurrence of congestion and guarantee stable quality in any situation; furthermore, this would defeat the purpose of the IP network that provides low-cost and handy services primarily intended for voice communication.
Another possible method would be to equip each terminal with a means for avoiding congestion, but equipping every terminal with such a function would limit the user's selection of terminals and would not be desirable from the service point of view; furthermore, this method is not generally practicable because the operating performance of the function between terminals must be guaranteed.